KAISER ALUMINUM CORP

To be considered for inclusion in our proxy statement for our 2026 annual meeting of stockholders, proposals of stockholders must be in writing and received by us no later than January 6, 2026. To be presented at the 2026 annual meeting of stockholders without inclusion in our proxy statement for such meeting, proposals of stockholders must be in writing and received by us no later than March 7, 2026 and no earlier than February 5, 2026, in accordance with procedures set forth in our bylaws. Such proposals should be mailed to Kaiser Aluminum Corporation, 1550 West McEwen Drive, Suite 500, Franklin, Tennessee 37067 and directed to the corporate secretary.

In addition to satisfying the foregoing requirements and other procedures set forth under our Bylaws, to comply with the universal proxy rules, stockholders who intend to solicit proxies in support of director nominees other than the Board’s nominees must provide notice that sets forth the information required by Rule 14a-19 of the Exchange Act (including a statement that such stockholder intends to solicit the holders of shares representing at least 67% of the voting power of the Company’s shares entitled to vote on the election of directors in support of nominees other than the Company’s nominees) no later than April 11, 2026 for the 2026 annual meeting; provided, however, that if the date of the 2026 annual meeting is changed by more than 30 calendar days from the anniversary of the Annual Meeting, then the notice must be provided by the later of 60 calendar days prior to the 2026 annual meeting or the 10 th calendar day following the day on which public announcement of the date of the 2026 annual meeting is first made.

By Order of the Board of Directors

John M. Donnan

Executive Vice President, Chief Administrative

Officer and General Counsel

Franklin, Tennessee

April 28, 2025

Appendix A

Reconciliation of Non-GAAP Measures - Consolidated

(Unaudited)

(In millions of dollars, except per share amounts)

The Proxy Statement contains certain non-GAAP financial measures. A “non-GAAP financial measure” is defined as a numerical measure of a company’s financial performance that excludes or includes amounts so as to be different than the most directly comparable measure calculated and presented in accordance with GAAP in the statements of income, balance sheets, or statements of cash flow of the Company. This Appendix A provides a reconciliation of non-GAAP financial measures to the most directly comparable financial measure. The non-GAAP financial measures used within the Proxy Statement are conversion revenue, Adjusted EBITDA, adjusted net income, and adjusted earnings per diluted share, which exclude non-run-rate items and ratios related thereto. “Non-run-rate” items are items that, while they may occur from period to period, are particularly material to results, impact costs primarily as a result of external market factors and may not occur in future periods if the same level of underlying performance were to occur. These measures are presented because management uses this information to monitor and evaluate financial results and trends and believes this information to also be useful for investors.